The recent cellular mobile communication involves using frequency allocation based on [one cell frequency reuse] which utilizes the same frequency band in all of the cells or the sectors in order to improve frequency available efficiency. In this case, at a cell boundary or a sector boundary, an SIR (Signal to Interference power Ratio) of the signal declines due to influence exerted by the same frequency interference from the neighboring cells or the neighboring sectors, resulting in such a problem that a communication throughput decreases.
A fast cell selection (Fast Cell Selection) method is under consideration as a method of improving the communication throughput at the cell boundary on a downlink to a mobile station from a base station (refer to Non-Patent document 1 given below).
The fast cell selection method is proposed for the first time as SSDT (Site Selection Diversity Transmission) (refer to Non-Patent document 2 given below). Note that a similar technology implemented between the sectors might be called fast sector selection, however, these are the same in terms of their principles. Accordingly, unless particularly specified, the cell can be construed as the sector in a way that gives a different reading, while the sector can be construed as the cell in the way of changing the wording.
FIG. 11 is a diagram representing the principle of the fast cell selection method. In the fast cell selection method, a mobile station MS1 existing in the vicinity of the cell boundary measures a propagation state of each cell and notifies the base station of the cell offering the optimal propagation state. Data, which should be transmitted to the mobile station MS1, is transmitted from only the base station in the plurality of base stations that forms the cell offering the optimal propagation state of which the mobile station notifies. A scheme of the fast cell selection method is not that the same information is transmitted simultaneously from the plurality of cells as by soft handover but that the cell exhibiting a good propagation state is invariably selected and used for the transmission. The fast cell selection method fast follows an alteration of propagation state by switching over the base station which transmits the data at high frequency on a slot basis illustrated in FIG. 11.
A base station control unit having a function of linking up operations between the base stations is employed for switching over the transmission slot at the high speed between the base stations. As in the case of the fast sector selection method, if a distance between the base stations (between the antennas) is short, the two base stations and the base station control unit in FIG. 11 can be actualized within one single apparatus. Thus, also in the case of the actualization within one single apparatus, respective function units realized by the base stations and the base station control unit in FIG. 11 need providing within the single apparatus. Accordingly, the same principle is applied to the fast sector selection method in such a case that the single base station configures a plurality of sectors.    [Non-Patent document 1] Morimoto, Abeta and Sawahashi, “Effect of Fast Cell Selection in Downlink Fast Packet Transmission”, SB-2-2, General Meeting of the Institute of Electronics, Information and Communication Engineers, March in 2002.    [Non-Patent document 2] H. Furukawa, K. Hamabe and A. Ushirokawa, “SSDT—Site Selection Diversity Transmission Power Control for CDMA Forward Link,” IEEE Journal on selected areas in communications, Vol. 18, No. 8, pp. 1546-1554, August in 2000.